Indeed, let \(X\)  be a complex projective or compact Kähler manifold with non-negative (resp., positive) sectional curvature. The bisectional curvature can be written as a positive linear combination of two sectional curvatures (e.g., see [1]}), hence the bisectional curvature of \(X\)  is non-negative (resp., positive).
This means (by definition) that the tangent bundle \(TX\)  is Griffiths semipositive (resp., positive). Furthermore, by [2]} (resp., [3]}), Griffiths semipositive (resp., positive) bundles are nef (resp., ample).
